This invention relates to armored cable.
Armored cable typically has a metal sheath enclosing one or more individually insulated conductors. The sheath may be formed of a helically interlocked continuous strip of metal, or of smooth or corrugated continuous metal tubing.
The National Electrical Code identifies two types of armored cable: xe2x80x9cType MCxe2x80x9d and xe2x80x9cType ACxe2x80x9d. In Type AC, the insulated conductors are individually wrapped with protective paper, and a bare ground wire extends the length of and touches the inside wall of the sheath.
In Type MC cable, the insulated conductors are not individually wrapped with paper; rather they are surrounded as a group with a paper or plastic insulating wrap. The ground wire is one of the individually insulated conductors and, thus, does not touch the inside wall of the sheath. While the internal configurations of Type MC and Type AC armored cables differ, they have similar external appearances (i.e., gray-colored metal).
Armored cable permits orderly wiring for various applications within a building (e.g., fire protection devices, lighting, motors). For example, wires of different sizes serving different applications may be grouped within different armored cables. Because the cables typically are installed near to each other, and because the cables look identical or similar, it is difficult to distinguish the different cables which serve different applications. The particular application associated with an armored cable may or may not be indicated by attaching an identification tag, stamping a code into the outer surface of the cable""s sheath, or writing (e.g., with an indelible marker) in relatively small print somewhere on the outer surface of the sheath.
In general, in one aspect, the invention features an armored cable sheath including a conductive tubular structure having an internal passage, an outer surface, a first end, and a second end. The internal passage is sized and configured to enclose one or more conductors. The tubular structure is made of a material having a first visual appearance. A pattern of visible indicia, of different visual appearance from the first visual appearance, is applied on the outer surface and is repeated along the length of the sheath.
Embodiments of the invention include the following features. The pattern has color, e.g., red, green, blue, or yellow and is repeated at regular intervals along the length of the sheath.
In some embodiments, the conductive tubular structure includes crowns and valleys of a helically wound strip and the pattern leaves exposed a substantial portion of the outer surface of the crowns, and also leaves exposed a substantial portion of the strip where edges of the strip along the crowns contact a surface of the strip at the valleys. The pattern, applied along the length of the strip, may be discontinuous, e.g., a sequence of spots. The pattern may be a non-conductive material, and may be of ink, dye, or paint.
In some embodiments, the tubular structure comprises a cylinder formed from a continuous piece of metal tubing, and the pattern is formed repeatedly along the length of the sheath. The cylinder may have one or more corrugated outer walls and may have a generally rectangular transverse cross-sectional configuration.
In general, in other aspects, the invention features a cable including one or more conductors enclosed within the sheath, and a set of armored cables having applied patterns of different visual appearance.
In general, in other aspects, the invention features methods of making an armored cable sheath which include applying visual indicia to the outer surface of a conductive tubular structure or to the strip from which it is made by helical winding.
By looking at the cable, one can easily determine the number of conductors, type of insulation, and/or type of cable, or the particular application. The premarking of various colored designs on the sheath saves time and reduces errors in handling, installing, inspecting, and maintaining the armored cable.
Other features and advantages of the invention will become apparent from the following description and from the claims.